1. Field of the Invention
The present invention relates to a screw compressor.
2. Description of the Related Art
In a conventional screw compressor having a pair of male and female screw rotors with rotor shafts disposed in the horizontal direction, a timing gear and bearings are mounted on each of the rotor shafts and are lubricated and cooled with oil to prevent damage thereof.
In connection with the related art, an oil bath method is mentioned as a general lubricating method used in case of low- or medium-speed rotation. In the oil bath method it is desirable to install an oil gauge and thereby make it possible to check the oil level easily so that the oil level lies at the center of a bottom roller in principle. However, when it is intended to adopt the oil bath method for lubrication of bearings and timing gears in a positive-displacement compressors such as, for example, a screw compressor, it may not always be possible to install an oil gauge at such a position as permits easy visual checking of the oil level due to, for example, a unique external shape of a bearing casing for accommodating the bearings and timing gears.
In Japanese Patent No. 2580020, compressed air is taken out from a casing of an air compressor and is conducted to a throttle portion of an oil mist producer, then with a negative pressure generated in the throttle portion, lubricating oil is sucked up and made into oil mist, then oil mist is fed for lubrication to bearings and timing gears accommodated within a casing. According to this conventional method it is possible to avoid exhaustion of the lubricating oil, but there remains the problem that the position of oil level cannot be confirmed.
In Japanese Patent Laid-Open No. 2003-148370, an oil level sensor is mounted within a casing of a scroll compressor, and when the oil level becomes lower than the position of the oil level sensor, a valve opens in accordance with a signal provided from the oil level sensor, and lubricating oil is supplied from an oil container which stores the lubricating oil. In the scroll compressor, however, rotor shafts are disposed in the vertical direction, and if the lubricating method is applied to a screw compressor with rotor shafts disposed in the horizontal direction, the oil level varies greatly due to splash of oil by timing gears and it is difficult to effect an accurate oil level detection.